Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$178.62	6.614%	$190.4339	$190.43	$190.45	$190.40
Purchase #2	$82.75	9.132%	$90.3067	$90.31	$90.30	$90.30
Purchase #3	$133.68	8.556%	$145.1177	$145.12	$145.10	$145.10
Purchase #4	$136.48	13.606%	$155.0495	$155.05	$155.05	$155.00
Purchase #5	$139.84	4.729%	$146.453	$146.45	$146.45	$146.50
Purchase #6	$18.52	8.567%	$20.1066	$20.11	$20.10	$20.10
Purchase #7	$250.58	11.858%	$280.2938	$280.29	$280.30	$280.30
7 purchase totals =	$940.47		$1,027.7612	$1,027.76	$1,027.75	$1,027.70